Digital output temperature and humidity sensor DHT11 - DHT22
NOTE: Available as both a plain component, or as an Electronic Brick. (Available here: )

See photos at right: Connections are (V)oltage, (S)ignal, (G)round. On the Electronic Brick: (S)Signal, (V)Voltage,(G)Ground

NOTE: Needs 4.7K to 10K pullup resistor from +5 to Signal pin (Electronic Brick version has it built-in). Connect to Arduino Digital pin, not Analog pin. (Manufacturer says this about distance/pullup): When the connecting cable is shorter than 20 metres, a 5K pull-up resistor is recommended; when the connecting cable is longer than 20 metres, choose a appropriate pull-up resistor as needed.

Test Software Sketch for DHT11 (Credits: THANKS to Rob Tillaart)

DETAILS: Before you can use an "Arduino Software Library", you must make it available by copying it into the correct "libraries" folder. See Libraries HowTo HERE
Here is a .ZIP file available with the DHT sensor library for easier installation:

NOTE: Lots of good information about the DHT software library on the Arduino "Playground" site HERE.
NOTE: After you install the DHTLIB Library, look in EXAMPLES for similar test sketches for DHT21, DHT22
NOTE: Set your Serial Monitor (click for Info) to 115200 (Lower right of window)

For an example of a Web Server that displays DHT11 sensor values, see THIS:EXAMPLE SKETCH: DHT11, Temp, Humidity, Time (from RTC) [Connection Diagram Below]
THANKS to David Loveridge
Note: Not Tested by Terry yet...